Abstract
Modified bases were introduced into pre‐tRNAs during in vitro RNA synthesis or by chemical modification. These RNAs were used as substrates for the catalytic M1 RNA and the RNase P holoenzyme from Schizosaccharomyces pombe. The synthetic approach permitted the insertion of 100% m7GTP into pre‐tRNAs and this resulted in complete inhibition of the specific 5′ processing reactions. Partially modified RNAs were obtained by chemical modifications of purines and uridines in the pre‐tRNAs. This allowed detailed analyses of specific bases excluded in the products. With pre‐tRNA(Ser) and initiator pre‐tRNA(Met), strong effects were observed in the T arm and weaker effects in the anticodon stem. Only minor base exclusions were detected in the acceptor stem of pre‐tRNA(Ser) and in the D arm of pre‐tRNA(Met).